In recent years, some liquid crystal display devices are equipped with a memory function corresponding to each pixel in order to reduce power consumption. Such a device is called, for example, a “memory liquid crystal display” or simply a “memory liquid crystal”. In general, the memory liquid crystal display is capable of holding one-bit data for each pixel, and performs image display using data held in memory when displaying the same image or an image that barely changes for a long period of time. In the memory liquid crystal display, when once data is written in the memory, the contents of the data written in the memory are held until the next update. Accordingly, little power is consumed during periods other than before and after a change in the contents of an image. As a result, power consumption is reduced compared to liquid crystal display devices without the memory function.
FIG. 23 is a block diagram illustrating a schematic configuration of a conventional memory liquid crystal display. This memory liquid crystal display is configured by a pixel memory portion 90, a gate driver 92 and a source driver 93 which are for driving the pixel memory portion 90, and a terminal portion 91 for externally receiving various signals and the like. The pixel memory portion 90, the terminal portion 91, the gate driver 92, and the source driver 93 are formed on a panel substrate 900. The pixel memory portion 90 is capable of holding one-bit data for each pixel, as described above. In such a configuration, by the operation of the gate driver 92 and the source driver 93, data corresponding to a display image is stored in memory corresponding to each pixel within the pixel memory portion 90. Then, the image is displayed on the basis of the data stored in the memory.
Note that in relevance to the present invention, Japanese Laid-Open Patent Publication No. 2007-286237 discloses an invention of a display device including pixel memory circuits configured as shown in FIG. 24. In this display device, one pixel memory circuit is provided for each pixel unit consisting of three, i.e., R, G, and B, subpixels, rather than for each of the R, G, and B subpixels. This inhibits an increase in circuit area and realizes low power consumption owing to drive using memory.